Fluorine-18 is a radioisotope of fluorine that is commonly used in medical imaging. It has a half-life of 109.8 minutes.

Fluorine-18 undergoes positron decay. Provide the complete balanced nuclear equation that describes this reaction.
What fraction of a sample of Fluorine-18 has decayed 4.0 hours after it was administered to a patient?
If a patient was administered 0.500g of Fluorine-18, what mass of Fluorine-18 remains radioactive 4.0 hours after it was administered?